PELTON WHEEL

 

PELTON WHEEL

• It is a Tangential flow impulse turbine.
• It is a high head turbine.
• It is a low specific speed turbine.
• It is a low discharge turbine.
• In this Turbine, inlet Pressure = Outlet Pressure = Atmospheric pressure.
• There is no problem of cavitation.

MAIN COMPONENTS: -

Fig.1 | Component of Pelton Wheel

Casing

Nozzle

Spear

Runner

Braking Jet

 

DESIGN PARAMETER: -

Jet Ratio (m) = [Dia. Of Pelton wheel (D) / Dia. of jet (d)]

No of Vane = 15 + (D/2d) = 15+ 0.5m

Width of Vane = 5d

Depth of Vane =1.2d

The maximum no. of jets generally employed on pelton wheel is 6.

WORK DONE & EFFECIENCY: -

Work done per second = ρAV₁ [V_w1 +V_w2] x u

Kinetic Energy of jet per second = 1/2mV₁² =1/2 (ρAV₁) V₁² =1/2 ρAV₁³

Hydraulic Efficiency (η_H) =W.D. /K.E. of jet

= [ρAV₁ (V_w1 +V_w2) x u] / (1/2 ρAV₁³)

η_H = [2(V_w1 +V_w2) x u] / V₁²

By putting the value of V_w1 & V_w2 from velocity triangle-

η_H = [2u(V₁-u)(1+cosФ)] / V₁²

By differentiating the above equation we will get the condition of maximum efficiency.

Condition of Maximum Efficiency – u = V₁ /2

Where, u = velocity of runner

V₁= Velocity of jet.

 

Maximum Hydraulic Efficiency (η_Max) = [1 + k cosФ] / 2

Where, K = V_r1/ V_r2

 

If K = 1(i.e. blade is smooth) and Ф = 15⁰, η_Max = 98.6%

η is maximum when speed ratio is 0.46.